Add explicit working folder; rename project from CadSearchGui to PrepStep

Working folder (phase 1): CSV/raw/step/step_finali all used to live split
across two different implicit locations (CSV in the "repo root" found by
walking up for CLAUDE.md, raw/step next to the input distinta file) with
neither shown to the user. That repo-root lookup also silently breaks once
the app runs as a standalone published exe on a machine with no repo/
CLAUDE.md at all. Replaced both with one explicit "cartella di lavoro",
auto-suggested (last used, remembered the same way as the DB path) and
changeable from phase 1, with no dependency on any repo marker file.

Rename: CadSearchGui was the working name from before the app had a
product identity; renamed folders, csproj files, namespace and the
AppData settings folder to PrepStep throughout, matching the exe name
already in use. Product-facing name stays "Cevolani StepPrep".

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

PrepStep/PrtMancantiForm.cs

@@ -0,0 +1,74 @@
+using System.Diagnostics;
+
+namespace PrepStep;
+
+/// <summary>Mostra l'esito della risoluzione ricorsiva dell'albero componenti: i PRT e i
+/// sotto-assiemi trovati nell'indice e già copiati in "raw" a partire dagli assiemi iniziali.</summary>
+public class PrtMancantiForm : Form
+{
+    public PrtMancantiForm(List<(string Codice, string Tipo, string Percorso)> righe, List<string> codiciNonTrovati, string cartellaRaw)
+    {
+        int numPrt = righe.Count(r => r.Tipo == "prt");
+        int numAsm = righe.Count(r => r.Tipo == "asm");
+
+        Text = "Componenti referenziati trovati";
+        ClientSize = new Size(720, 440);
+        StartPosition = FormStartPosition.CenterParent;
+        Font = new Font("Segoe UI", 9.5f);
+
+        var lblInfo = new Label
+        {
+            Dock = DockStyle.Top,
+            AutoSize = true,
+            Padding = new Padding(12, 8, 12, 8),
+            Text = $"Copiati in \"{cartellaRaw}\": {numPrt} PRT e {numAsm} sotto-assiemi trovati nell'indice."
+                + (codiciNonTrovati.Count > 0
+                    ? $" {codiciNonTrovati.Count} codici referenziati non corrispondono a nessun file indicizzato "
+                      + "(righe 'non trovato' sotto: possono essere disegni, componenti davvero mancanti, "
+                      + "o falsi positivi della scansione)."
+                    : ""),
+        };
+
+        var grid = new DataGridView
+        {
+            Dock = DockStyle.Fill,
+            ReadOnly = true,
+            AllowUserToAddRows = false,
+            AllowUserToDeleteRows = false,
+            RowHeadersVisible = false,
+            SelectionMode = DataGridViewSelectionMode.FullRowSelect,
+            AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.Fill,
+        };
+        grid.Columns.Add("codice", "Codice");
+        grid.Columns.Add("tipo", "Tipo");
+        grid.Columns.Add("percorso", "Percorso CAD");
+        grid.Columns["codice"]!.FillWeight = 20;
+        grid.Columns["tipo"]!.FillWeight = 10;
+        grid.Columns["percorso"]!.FillWeight = 70;
+        foreach (var (codice, tipo, percorso) in righe.OrderBy(r => r.Tipo).ThenBy(r => r.Codice))
+        {
+            grid.Rows.Add(codice, tipo, percorso);
+        }
+        foreach (var codice in codiciNonTrovati.OrderBy(c => c))
+        {
+            int i = grid.Rows.Add(codice, "non trovato", "");
+            grid.Rows[i].DefaultCellStyle.ForeColor = Color.DarkRed;
+        }
+
+        var btnApriCartella = new Button { Text = "Apri cartella raw", Dock = DockStyle.Bottom, Height = 34 };
+        UiStile.Secondario(btnApriCartella);
+        btnApriCartella.Click += (_, _) =>
+        {
+            try { Process.Start("explorer.exe", cartellaRaw); }
+            catch (Exception ex)
+            {
+                MessageBox.Show(this, $"Impossibile aprire Esplora risorse:\n{ex.Message}", "Errore",
+                    MessageBoxButtons.OK, MessageBoxIcon.Error);
+            }
+        };
+
+        Controls.Add(grid);
+        Controls.Add(lblInfo);
+        Controls.Add(btnApriCartella);
+    }
+}